This invention relates generally to electrostatic image transfers and, more specifically, to a conductive intermediate transfer surface and the method of employing that conductive intermediate transfer surface in a color printing process employing a liquid toner.
Elastomeric transfer surfaces have been used in electrophotographic copiers. Early efforts employed an electrophotographic copier with a rotatable photoconductive drum that transferred a dry toner developed image to a silicone elastomer transfer belt that was part of a transfer and fusing system. This was employed in combination with a radiant fuser and paper transport system to provide a high speed copier.
Another related system employed an intermediate transfer drum which received the dry toner developed image from a rotatable drum whose surface was coated with a photoconductor. The intermediate transfer drum utilized a support material such as aluminum and had its surface coated with a suitable conductive or non-conductive silicone rubber having low specific heat that was applied in a thin layer. These intermediate transfer surfaces were described as having smooth surfaces of low surface free energy and a hardness of from 3 to 70 durometers.
Compositions designed specifically for use as thermally conductive elastomers in a fuser roller for electrostatic copying machines were developed by the Dow Corning Corporation. The compositions were thermally conductive polyorganosiloxane elastomers that possessed high abrasion resistance, low durometer hardness and high heat conductivity.
Xerox Corporation developed an elastomeric intermediate transfer surface that was either formed into a belt or was formed on the surface of a drum as part of a process to transfer a dry powder xerographic image from a photoconductive surface to a final support surface, such as paper. Heat and pressure were utilized to transfer the developed powder image from the intermediate elastomeric transfer surface to the paper.
All of these prior approaches utilized a dry powder toner that was contact or pressure transferred from the photoconductive surface to the intermediate transfer surface and then to the final receiving surface. These approaches were susceptible to image distortion during the transfer from the photoconductor because of the pressure or contact involved in the transfer step. They also transferred less than 100% of the toner particles from the intermediate transfer surface to the final receiving surface. None of these approaches attempted to use a liquid toner to improve the resolution of the transferred image. The use of liquid toners, because of the suspension of the toner particles in non-polar insulating solvents that are usually mixtures of branched aliphatic hydrocarbons, will cause a conductive silicone-based elastomer to swell upon exposure and become very dielectric. These results affect the quality of the transferred image and reduce the ability to electrostatically transfer the charged toner particles. The consistency of the intermediate transfer surface upon prolonged exposure to these solvents will change to that of a gel.
Subsequently, a system employing a liquid toner has been developed to transfer a liquid developed image from a photoconductor to a copy sheet via an intermediate transfer surface from which the carrier liquid is roller squeezed or removed by infrared heating to be substantially free of carrier liquid prior to the final image transfer to the copy sheet. However, this does not remove all of the solvent from the copy sheet, since solvent is still present in the image areas in order to achieve electrostatic image transfer. The intermediate transfer surface is formed from a material described as non-absorbing and resilient, but transfer from the photoconductor to the intermediate transfer surface is effected by contact pressure and the intermediate transfer surface is deformed by contact with the toner particles in the image areas to achieve the transfer from the photoconductor covered drum to the intermediate transfer surface. This negatively affects the quality of the transferred image as described previously.
These problems are solved in the process of the present invention and in the design of the intermediate transfer surface by providing a conductive intermediate transfer surface formed of conductive fluoroelastomer material that can reversibly deform and is resistant to solvent and heat. The conductive intermediate transfer surface which can also be a conductive fluoropolymer, is used in a two step transfer process that initially electrostatically transfers a liquid toner developed image from a master surface through a liquid-filled gap to the intermediate transfer surface and then by contact transfer to the final receiving surface, such as paper. No carrier liquid needs to be transferred to the final receiving surface.